Electronic and Thermal Properties of Si-doped InSe Layered Chalcogenides

Layered metal chalcogenide materials have attracted significant attention as potential thermoelectric materials owing to their intrinsic low thermal conductivity because of their weak atomic bonding between layers. Indium selenide (InSe) crystals are known to have a low thermal conductivity in the range ~ 0.37 - 1.2 Wm⁻¹K⁻¹, and their intrinsic carrier concentration is quite low (~ 10¹⁴ cm⁻³) owing to a relatively large bandgap of 1.2 eV. Therefore, InSe-based materials can be good candidates for thermoelectric materials if the carrier concentration can be increased by appropriate doping. In this work, we investigated the electronic and thermal properties of a series of Si-doped InSe polycrystalline samples In_1−xSi_xSe with nominal x = 0.01, 0.02, 0.04, and 0.08. The cation substitution with Si increased the electrical conductivity of InSe to 8.5 S/cm at 795 K while decreasing the activation energy for the electrical conductivity. The negative Seebeck coefficient increased as Si doping increased, resulting in a significant enhancement in the power factor. A slight reduction in thermal conductivity was also observed with doping. Consequently, the expected thermoelectric figure of merit zT value was expected as high as ~ 0.16 for x = 0.08 at 765 K, which offers the possibility of InSe-based thermoelectric materials.